Off quadrature biasing of mach zehnder modulator for improved osnr performance

ABSTRACT

An integrated optical modulator device. The device can include a driver module coupled to an optical modulator. The optical modulator is characterized by a raised cosine transfer function. This optical modulator can be coupled to a light source and a bias control module, which is configured to apply an off-quadrature bias to the optical modulator. This bias can be accomplished by applying an inverse of the modulator transfer function to the optical modulator in order to minimize a noise variance. This compression function can result in an optimized increased top eye opening for a signal associated with the optical modulator. Furthermore, the optical modulator can be coupled to an EDFA (Erbium Doped Fiber Amplifier) that is coupled to a filter coupled an O/E (Optical-to-Electrical) receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims priority to U.S.application Ser. No. 14/706,908 filed on May 7, 2015, and isincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to telecommunication techniques andintegrated circuit (IC) devices. More specifically, various embodimentsof the present invention provide an integrated optical modulator device.

Over the last few decades, the use of communication networks hasexploded. In the early days of the Internet, popular applications werelimited to emails, bulletin board, and mostly informational andtext-based web page surfing, and the amount of data transferred wasrelatively small. Today, Internet and mobile applications demand a hugeamount of bandwidth for transferring photo, video, music, and othermultimedia files. For example, a social network like Facebook processesmore than 500 TB of data daily. With such high demands on data and datatransfer, existing data communication systems need to be improved toaddress these needs.

CMOS technology is commonly used to design communication systemsimplementing Optical Fiber Links. As CMOS technology is scaled down tomake circuits and systems run at higher speed and occupy smaller chip(die) area, the operating supply voltage is reduced for lower powerconsumption. Conventional FET transistors in deep-submicron CMOSprocesses have very low breakdown voltage as a result the operatingsupply voltage is maintained around 1 Volt. The Photo-detectors (PD)used in 28 G and 10 G Optical Receivers require a bias voltage of morethan 2 Volts across the anode and cathode nodes of the PD for betterphoto-current responsivity. These limitations provide significantchallenges to the continued improvement of communication systems scalingand performance.

There have been many types of communication systems and methods.Unfortunately, they have been inadequate for various applications.Therefore, improved communication systems and methods are desired.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to telecommunication techniques andintegrated circuit (IC) devices. More specifically, various embodimentsof the present invention provide an off-quadrature biased integratedoptical modulator device.

In optically amplified systems, the dominant noise source is the opticalamplifier, which is typically an EDFA (Erbium Doped Fiber Amplifier) inDWDM (Dense Wavelength Division Multiplexing) systems. The majorcomponent of the amplifier noise in such systems is thesignal-spontaneous beat noise, which is due to the interference betweenthe amplified signal and ASE (Amplified Spontaneous Emission).Considering that the noise power is relatively small in beat noise, thisnoise will dominate when the signal power is at its highest. Conversely,if there is no signal, there is no beat noise.

In an example, the highest noise and largest eye closure happens at thetop level for a 4-level PAM (Pulse-Amplitude Modulation) signal or the“1” level in the NRZ modulation format. More specifically, if thedifferent levels of the PAM-4 (4-level PAM) signal are set up in anequally spaced configuration, the noise impacts the top level most, andleads to the greatest eye closure. However, if the individual levels canbe reshaped such that the largest opening is at the top level, then thenoise contribution between the various levels can be equalized toimprove system performance. This technique can be applied to 4-level PAMsystems, 8-level PAM systems, 16-level PAM systems, and the like.

The present invention provides several embodiments of an electro-opticalmodulator with improved OSNR (Optical Signal-to-Noise Ratio) by theapplication of an off-quadrature bias. This application is counterintuitive, as typical applications of an optical modulator, such as anMZM (Mach-Zehnder Modulator) or the like, are biased at quadrature (50%point in a DC characteristic plot) to produce the maximum signal swing.However, by biasing the optical modulator off-quadrature and sacrificinga portion of the signal swing, the optical modulator exhibits a muchimproved OSNR in an optically amplified system.

In an embodiment, the present invention provides an optical modulatordevice. This device can include a driver module coupled to an opticalmodulator. The optical transfer function of a Mach Zehnderinterferometer optical modulator is characterized by a raised cosine orsine transfer function. This optical modulator can be coupled to a lightsource and a bias control module, which is configured to apply anoff-quadrature bias to the optical modulator. This bias can beaccomplished by applying a DC bias function to the optical modulator inorder to minimize a noise variance that is proportional to 2√{squareroot over (nΔP_(ASE))}, wherein nΔ is signal level n and P_(ASE) isAmplified Spontaneous Emission Power. This compression function canresult in an optimized increased top eye opening for a signal associatedwith the optical modulator. Furthermore, the optical modulator can becoupled to an EDFA (Erbium Doped Fiber Amplifier) that is coupled to afilter coupled an O/E (Optical-to-Electrical) receiver. Those ofordinary skill in the art will recognize other variations,modifications, and alternatives.

Many benefits are recognized through various embodiments of the presentinvention. Such benefits include improved system performance due tooff-quadrature biasing of an optical modulator device. Embodiments ofthis off-quadrature bias configuration provide improvements to OSNR(Optical Signal-to-Noise Ratio) of an optical system. Other benefitswill be recognized by those of ordinary skill in the art that themechanisms described can be applied to other optical systems as well.

The present invention achieves these benefits and others in the contextof known data transmission and optically amplified technologies.However, a further understanding of the nature and advantages of thepresent invention may be realized by reference to the latter portions ofthe specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following diagrams are merely examples, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many other variations, modifications, and alternatives.It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this process andscope of the appended claims.

FIG. 1 is a simplified block diagram of an integrated optical modulatordevice according to an embodiment of the present invention.

FIG. 2A is a simplified graph showing a comparison of quadrature biasversus off-quadrature bias of a modulator transfer function for anoptically amplified system according to an embodiment of the presentinvention.

FIG. 2B is a simplified graph showing the OSNR (Optical Signal-to-NoiseRatio) for an off-quadrature biased optical modulator device and aquadrature biased optical modulator device according to an embodiment ofthe present invention.

FIG. 3 is a simplified graph representing a signal output for aquadrature biased optical modulator device according to an embodiment ofthe present invention.

FIG. 4 is a simplified graph representing a signal output for anoff-quadrature biased optical modulator device according to anembodiment of the present invention.

FIG. 5 is a simplified graph showing the OSNR for optical modulatordevices configured at various bias points according to embodiments ofthe present invention.

FIG. 6 is a simplified diagram of a single hybrid die (Both electricaland optics devices are fabricated on a single hybrid die) according toan embodiment of the present invention.

FIG. 7 is a simplified diagram of a multi-chip module according to anembodiment of the present invention.

FIG. 8 is a simplified diagram of an electrical silicon die blockaccording to an embodiment of the present invention.

FIG. 9 is a simplified diagram of high speed serial link block accordingto an embodiment of the present invention.

FIG. 10 is a simplified diagram of a digital processing/signalpre-distortion block according to an embodiment of the presentinvention.

FIG. 11 is a simplified diagram of an electrical laser driver and TLAblock diagram according to an embodiment of the present invention.

FIG. 12 is a simplified diagram of a silicon photonic block diagramaccording to an embodiment of the present invention.

FIG. 13 is a simplified block diagram of a multi-chip module accordingto an alternative embodiment of the present invention.

FIG. 14 is a simplified block diagram of data flow according to anembodiment of the present invention.

FIG. 15 is a simplified diagram illustrating a redundant laserconfiguration at a drive stage according to an embodiment of the presentinvention.

FIG. 16 is a simplified diagram illustrating a built-in self test usingan optical loop back according to an embodiment of the presentinvention.

FIG. 17 is a simplified diagram illustrating a built-in self testconfigured for optical testing according to an embodiment of the presentinvention.

FIG. 18 is a simplified diagram illustrating wavelength tuningconfigured to silicon photonic device according to an embodiment of thepresent invention.

FIG. 19 is a simplified block diagram of an interface for a siliconphotonics device according to an embodiment of the present invention.

FIG. 20 is a simplified diagram illustrating a laser configuration at atransmitter side of a silicon photonics device according to anembodiment of the present invention.

FIG. 21 is a simplified diagram illustrating a laser configuration at areceiver side of a silicon photonics device according to an embodimentof the present invention.

FIGS. 22 and 23 are simplified diagrams illustrating a hybrid lightsource for a silicon photonics device according to an embodiment of thepresent invention.

FIG. 24 is a simplified diagram illustrating a wavelength control andlocking configuration with a silicon photonic device according to anembodiment of the present invention.

FIG. 25 is a simplified diagram illustrating a wavelength control andlocking configuration with a silicon photonics device according to analternative embodiment of the present invention.

You need to include this in the figure to explain what off-quadraturebias means. And also why you have to bias the modulator towards the nullpoint and not the maximum transmission point for this technique to work.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to telecommunication techniques andintegrated circuit (IC) devices. More specifically, various embodimentsof the present invention provide an off-quadrature biased integratedoptical modulator device. With the off-quadrature bias, the behavior ofthe optical modulator can be modified in order to minimize noise andimprove system performance.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

In the following detailed description, numerous specific details are setforth in order to provide a more thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without necessarily being limitedto these specific details. In other instances, well-known structures anddevices are shown in block diagram form, rather than in detail, in orderto avoid obscuring the present invention.

The reader's attention is directed to all papers and documents which arefiled concurrently with this specification and which are open to publicinspection with this specification, and the contents of all such papersand documents are incorporated herein by reference. All the featuresdisclosed in this specification, (including any accompanying claims,abstract, and drawings) may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

Please note, if used, the labels left, right, front, back, top, bottom,forward, reverse, clockwise and counter clockwise have been used forconvenience purposes only and are not intended to imply any particularfixed direction. Instead, they are used to reflect relative locationsand/or directions between various portions of an object.

In optically amplified systems, the dominant noise source is the opticalamplifier, which is typically an EDFA (Erbium Doped Fiber Amplifier) inDWDM (Dense Wavelength Division Multiplexing) systems. The majorcomponent of the amplifier noise in such systems is thesignal-spontaneous beat noise, which is due to the interference betweenthe amplified signal and ASE (Amplified Spontaneous Emission).Considering that the noise power is relatively small in beat noise, thisnoise will dominate when the signal power is at its highest (e.g.highest light intensity). Conversely, if there is no signal, there is nobeat noise.

In an example, the highest noise and largest eye closure happens at thetop level for a 4-level PAM (Pulse-Amplitude Modulation) signal. Morespecifically, if the different levels of the PAM-4 (4-level PAM) signalare set up in an equally spaced configuration, the noise impacts the toplevel and leads to the greatest eye closure. However, if the individuallevels can be reshaped such that the largest opening is at the toplevel, then the noise contribution between the various levels can beequalized to improve system performance. This technique can be appliedto 4-level PAM systems, 8-level PAM systems, 16-level PAM systems, andthe like.

In one or more embodiments, the present invention provides anelectro-optical modulator with improved OSNR (Optical Signal-to-NoiseRatio) by the application of an off-quadrature bias. This application iscounter intuitive, as typical applications of an optical modulator, suchas an MZM (Mach-Zehnder Modulator) or the like, are biased at quadrature(50% point in a DC characteristic plot) to produce the maximum signalswing. However, by biasing the optical modulator off-quadrature andsacrificing a portion of the signal swing, the optical modulatorexhibits a much improved OSNR. The following discussion of the figureswill give examples of optical modulator devices and its method ofoperation.

FIG. 1 is a simplified block diagram of an integrated optical modulatordevice according to an embodiment of the present invention. As shown,optical modulator device 100 is configured in a test configurationcoupled to a signal generator 110 and an oscilloscope 111. The signalgenerator 110 can be configured to provide, by an RF cable, theoscilloscope 111 a 10 MHz reference signal, or other reference signaldepending upon application. The signal generator 110 can be an AWG(Arbitrary Waveform Generator) 110, such as a 72 Gb/s AWG, or the like.The oscilloscope 111 can be an RT (Real-Time) scope, such as a 63 GHz RTScope, or the like. This test configuration allows for testing of theoptical modulator device by controlling inputs and recording outputs.

In an embodiment, the optical modulator device 100 can include a driver120 coupled to an optical modulator 130. The driver 120 can be adifferential input, single-ended output, variable gain, linear driver,which can receive a differential input from the AWG 110 by RF cables andtransmit the signal output to the optical modulator 130. A light source131 and a bias control module 132 can both be coupled to the opticalmodulator 130. In an example, the optical modulator 130 can be an MZM,or the like, and the light source 131 can be a laser module, an ITLA(Integrable Tunable Laser Assembly), or the like.

In a specific embodiment, the optical modulator driver 120, the lightsource 131, and the bias control module 132 all feed inputs viainterconnections to the optical modulator 130. The interconnectionbetween the driver 120 and the optical modulator 130 can be an RF (RadioFrequency) cable and the interconnection between the bias control module132 and the signal relay module 130 can be a DC (Direct Current)electrical cable. Also, the interconnection between the light source 131and the optical modulator 130 can be an optical fiber cable.

In an embodiment, the optical modulator 130 can be coupled to an EDFA(Erbium-doped Fiber Amplifier) 140, which can be coupled to a tunableoptical filter 150. The optical filter 150 can be coupled to an O/E(Optical-to-Electrical) receiver 160. The O/E receiver 160 can becoupled to the oscilloscope 111. The interconnections from the O/Ereceiver 160 can be RF cables providing a differential output to thescope 111. Also, an OSA (Optical Spectrum Analyzer) 112 can be coupledto the EDFA 140 to measure the EDFA parameters. The OSA 112 can beconfigured to the EDFA 140 by a 10/90 tap coupler, which directs 10% tothe output and 90% to the gain medium.

In a specific embodiment, the signal relay module 130 can be coupled toa first VOA (Variable Optical Attenuator) 141 to the EDFA 140 and thento a second VOA 142, which is coupled to the tunable optical filter 150.The interconnections between these modules can be optical fiberscharacterized by 0, 10, or 20 km SMF (Single-Mode Fiber). Those ofordinary skill in the art will recognize other variations,modifications, and alternatives.

As described previously, as aspect of the present invention is to biasthe optical modulator off-quadrature in order to obtain a much improvedor optimal OSNR. The optical modulator 130 is characterized by a raisedcosine or sine transfer function, which can be represented by theequation:

${\frac{1}{2}\left\lbrack {1 + {\sin \left\lbrack {\frac{v}{v_{pi}}\pi} \right\rbrack}} \right\rbrack},$

where v is the voltage input and v_(pi) is the voltage needed to reachphase pi. This is to say that the DC transfer function of the modulatorexhibits the behavior of a sinusoidal curve having phase characteristicof a cosine function with an average value or approximately 0.5.

In order to achieve the expansion of the top level in the PAM-4 signalexample, a DC bias function can be applied via the bias control module132 to the optical modulator. A method of expanding the top level of thePAM-4 signal is to apply a DC bias compression function to compress thelower levels of the PAM-4 signal. In a specific embodiment, thiscompression function is characterized by an inverse raised sinefunction, an inverse of the transfer function, or the like. In the DCtransfer curve, this compression function squeezes the bottom half ofthe sinusoid curve, which can result in a more flattened trough.

The result of this compression function is the compression of the bottomlevel of the PAM-4 signal and the expansion of the top level of thePAM-4 signal. This result is desirable due to the increased eye openingat the top level, which suffers from the most eye closure, and decreasedeye opening at the bottom level, which suffers from the least eyeclosure. An example of the improvement to the OSNR of an opticalmodulator is shown in the graph of FIG. 2B. Additionally, FIGS. 3 and 4show the characteristic difference in a PAM-4 signal between aquadrature biased optical modulator and an off-quadrature biased opticalmodulator according an embodiment of the present invention.

FIG. 2A is a simplified graph showing a comparison of quadrature biasversus off-quadrature bias of a modulator transfer function for anoptically amplified system according to an embodiment of the presentinvention. Graph 201 illustrates a modulator transfer curve with aquadrature bias point and an off-quadrature bias point marked on thecurve. As discussed previously, a bias compression function can beapplied to an optical modulator to expand the top level of an opticalsignal (e.g. PAM-4) by compressing the bottom level. It is important tonote that in biasing the optical modulator to expand the top signallevel, the bias function must be towards the downwards direction ortowards the null point, which is to compress the bottom or the troughsof the DC transfer curve. In applied in the upwards direction or themaximum transmission point, the top level would be compressed instead.This result is highly undesirable as there would be greater eye closureas the top level, which already suffers from the greatest eye closure.

FIG. 2B is a simplified graph showing the system Bit Error Rate vs. OSNR(Optical Signal-to-Noise Ratio) for an off-quadrature biased opticalmodulator device and a quadrature biased optical modulator deviceaccording to an embodiment of the present invention. As shown, the graph202 displays bit error rate, labeled as log 10(Pe), over OSNR measuredin dB (decibels). The “equispaced power levels configuration” isrepresented by the curve marked by “X”, and the “unequal power levels byoffset bias point” configuration is represented by the curve marked by“O”. In this example, a 3.2 dB improvement in OSNR is obtained by use ofthe offset bias.

FIG. 3 is a simplified graph representing a signal output for aquadrature biased optical modulator device according to an embodiment ofthe present invention. As shown, the graph 300 shows an example PAM-4(4-level Pulse Amplitude Modulation) signal according to the equispacedpower levels configuration measured in dBm (decibel-milliwatts) oversample point number. Here, the PAM-4 signal displays four signal levelswith three equally spaced eye-opening regions. This is thecharacteristic behavior of a Mach Zehnder Modulator biased atquadrature. FIG. 3 can represent the “equispaced power levels”configuration of FIG. 2.

In order to determine the optimal bias function, the signal noisebehavior for an optical modulator can be determined to minimize thenoise at the top level. According to an embodiment of the presentinvention, the noise related to ASE of signal level n of an opticalmodulator was determined to be proportional to 2√{square root over(nΔP_(ASE))}. Considering the PAM-4 signal example, the noise variancesfor each of the four signal amplitude levels can be represented by thefollowing equations:

At signal level 0, σ₀=0,

At signal level Δ, σ₁=2√{square root over (ΔP _(ASE,R×BW))},

At signal level 2Δ, σ₂=√{square root over (2ΔP _(ASE,R×BW))},

At signal level 3Δ, σ₃=2√{square root over (3ΔP _(ASE,R×BW))},

where P_(ASE,R×BW) is the Amplified Spontaneous Emission Power of thereceiver bandwidth.

Thus, an optical modulator can be biased using a bias control module,such as the one shown in FIG. 1, to compress the bottom level or levelsof an optical signal to expand the top level or levels in order tominimize the overall signal noise, which is represented by the term2√{square root over (nΔP_(ASE))}. In a specific embodiment, theindividual levels of an optical signal can be reshaped such that thelargest eye opening is at the top level and the noise contributionbetween the various levels are equalized to improve overall systemperformance.

FIG. 4 is a simplified graph representing a signal output for anoff-quadrature biased optical modulator device according to anembodiment of the present invention. As shown, the graph 400 shows anexample PAM4 signal according to the unequal power levels by offset biaspoint configuration. Here, the PAM4 signal displays four signal levelswith three eye-openings with the top being expanded and the bottom beingcompressed. FIG. 4 can represent the “unequal power levels”configuration of FIG. 2.

FIG. 5 is a simplified graph showing the OSNR for optical modulatordevices configured at various bias points according to embodiments ofthe present invention. As shown, the graph 500 shows the result from amodulator bias point sweep measuring BER (Bit Error Rate) over OSNR.Here, bias voltage levels from 3.1V to 3.9V are displayed with each testlevel represented in the key to the lower left of the graph. In thisexample, a 2.5 dB improvement over the quadrature bias was found in withan off-quadrature bias of about 14 degrees (corresponding to the 3.7Vbias). The off-quadrature bias can be further optimized depending uponapplication.

In an embodiment, the present invention provides an optical modulatordevice. The device can include an MZM driver coupled to an MZM. The MZMis characterized by a raised cosine or sine transfer function and isconfigured for a PAM (Pulse Amplitude Modulation) signal having at leasta top eye opening region and a bottom eye opening region. The MZM can becoupled to a light source and a bias control module, which is configuredto apply an off-quadrature bias to the optical modulator device. A firstVOA coupled to the MZM, and an EDFA coupled to the first VOA and asecond VOA. Also, a tunable optical filter can be coupled to the secondVOA and an O/E receiver coupled to the filter.

In a specific embodiment, the bias control module is configured toimprove an OSNR of the optical modulator device by applying anoff-quadrature bias to the optical modulator device. The bias controlmodule is configured to apply the off-quadrature bias to the opticalmodulator device a DC compression function, which can be an inverse ofthe transfer function. This compression function is applied to theoptical modulator in order to minimize a noise variance associated withthe PAM signal that is proportional to 2√{square root over (nΔP_(ASE))},where nΔ is signal level n and P_(ASE) is Amplified Spontaneous EmissionPower. Furthermore, the bias control module is configured to apply anoff-quadrature bias to the optical modulator such that the top eyeopening is expanded and the bottom eye opening is compressed and a noisecontribution associated with the noise variance for each level of thePAM signal is equalized.

In a specific embodiment, the MZM driver module is configured for aPAM-4 signal modulation characterized by four discrete pulse amplitudelevels, including first through fourth amplitude levels, and three eyeopening levels, including top, middle, and bottom eye openings. This MZMdriver can be a differential input, single-ended output, variable gain,linear driver. Those of ordinary skill in the art will recognize othervariations, modifications, and alternatives.

Many benefits are recognized through various embodiments of the presentinvention. Such benefits include improved system performance due tooff-quadrature biasing of an optical modulator device. Embodiments ofthis off-quadrature bias configuration provide improvements to OSNR(Optical Signal-to-Noise Ratio) of an optical system. Other benefitswill be recognized by those of ordinary skill in the art that themechanisms described can be applied to other optical systems as well.The following description of figures provides additional informationrelating to an integrated optical system which can incorporate theoptical modulator described previously.

FIG. 6 is a simplified diagram of a single hybrid die (Both electricaland optics devices are fabricated on a single hybrid die) according toan embodiment of the present invention. In an example, the presentdevice 600 comprises a single hybrid communication module made ofsilicon material. The module comprises a substrate member 610 having asurface region, an electrical silicon chip 620 overlying a first portionof the surface region, an silicon photonics device 630 overlying asecond portion of the surface region, a communication bus coupledbetween the electrical silicon chip and the silicon photonics device, anoptical interface 621 coupled to the silicon photonics device 630, andan electrical interface 621 coupled to the electrical silicon die 620.

FIG. 7 is a simplified diagram of a multi-chip module according to anembodiment of the present invention. In an example, the present device700 comprises a single hybrid communication module. The module comprisesa substrate member 710 having a surface region, which can be a printedcircuit board or other member. The module comprises an electricalsilicon chip 720 overlying a first portion of the surface region, asilicon photonics 730 device overlying a second portion of the surfaceregion, a communication bus 740 coupled between the electrical siliconchip and the silicon photonics device, an optical interface 731 coupledto the silicon photonics device 730, and an electrical interface 721coupled to the electrical silicon die 720.

FIG. 8 is a simplified diagram of an electrical silicon die blockaccording to an embodiment of the present invention. As shown, thepresent device 800 can include a high speed serial link block 810, adigital signal processing/signal pre-distortion block 820, and a lasermodulator driver transimpedance amplifier (TIA) 830, or other likedevices. In an embodiment, the high speed serial link can include TXline, RX line, and PLL (Phase-Locked Loop) implementations. The seriallink block 810 can be coupled to the signal processing module 820, whichcan be coupled to transimpedance amplifier 830.

FIG. 9 is a simplified diagram of high speed serial link block accordingto an embodiment of the present invention. As shown, the serial linkblock 900 can include a core 910, which can be an all digital SERDEScore. The core 910 can include an all digital PLL 920, and all digitalfast lock CDR 930 (Lock within 10 bits), and a digital calibrations anddigital logics block 940. The core 910 can be coupled to multiple bitsflash samplers 950. In a specific embodiment, the serial link block 810of FIG. 8 can be configured like block 900.

FIG. 10 is a simplified diagram of a digital processing/signalpre-distortion block according to an embodiment of the presentinvention. As shown, the digital processing/signal pre-distortion block1000 can include an error encoding/decoding block 1010, an opticaldistortion electrical compensation (EDC) block 1020, and a modulationconversion block 1030. In an embodiment, the encoding/decoding block1010 can be coupled to the EDC block 1020, which is coupled to themodulation conversion block 1030. In a specific embodiment, themodulation conversion block 1030 can be configured to convert NRZ tomultiple levels PAM. The TIA block 830 of FIG. 8 can be configured likeblock 1000.

FIG. 11 is a simplified diagram of an electrical laser driver and TIAblock diagram according to an embodiment of the present invention. Asshown, the laser driver and TIA block 1100 can include an edge ratecontrol circuit 1110 coupled to a swing and common mode voltageadjustable driver 1120. The driver and TIA block 1100 can also include alimiting amplifier 1130 coupled to a TIA 1140, which can be coupled toan input bandwidth control block 1150. Other configurations may be usedas well.

FIG. 12 is a simplified diagram of a silicon photonic block diagramaccording to an embodiment of the present invention. As shown, thesilicon photonics block 1200 can include a substrate 1210, a continuouswave (CW) distributed feedback (DFB) laser block 1220, anelectro-absorption modulator or MZ modulator 1230, control loops 1240,and photo diode detectors 1250. Other variations, modifications, andalternatives will be recounized by those skilled in the art.

FIG. 13 is a simplified block diagram of a multi-chip module accordingto an alternative embodiment of the present invention. As shown, thepresent invention includes an integrated system on chip device. Thedevice 1300 is configured on a single silicon substrate member. Thedevice has a data input/output interface provided on the substratemember and configured for a predefined data rate and protocol. Thedevice has an input/output block 1320 provided on the substrate memberand coupled to the data input/output interface. In an example, theinput/output block 1320 comprises a SerDes block, a CDR block, acompensation block, and an equalizer block, among others. The device hasa signal processing block 1310 provided on the substrate member andcoupled to the input/output block 1320. In an example, the signalprocessing block 1310 is configured to the input/output block 1320 usinga bi-direction bus in an intermediary protocol. The device has a drivermodule 1360 provided on the substrate member and coupled to the signalprocessing block. In an example, the driver module 1360 is coupled tothe signal processing block 1310 using a uni-directional multi-lane bus.In an example, the device has a driver interface provided on thesubstrate member and coupled to the driver module 1360 and configured tobe coupled to a silicon photonics device 1370. In an example, the driverinterface is configured to transmit output data in either an amplitudemodulation format or a combination of phase/amplitude modulation formator a phase modulation format. In an example, the device has a receivermodule 1350 comprising a TIA block provided on the substrate member andto be coupled to the silicon photonics device 1370 using predefinedmodulation format, and configured to the digital signal processing block1310 to communicate information to the input output block 1320 fortransmission through the data input/output interface. In an example, thedevice has a communication block 1330 provided on the substrate memberand operably coupled to the input/output block 1320, the digital signalprocessing block 1310, the driver block 1360, and the receiver block1350, among others. The device has a communication interface coupled tothe communication block 1330. The device has a control block 1340provided on the substrate member and coupled to the communication block1330.

In an example, the signal processing block 1310 comprises a FEC block, adigital signal processing block, a framing block, a protocol block, anda redundancy block, among others. The driver module 1360 is selectedfrom a current drive or a voltage driver in an example. In an example,the driver module is a differential driver or the like. In an example,the silicon photonics device 1370 is selected from an electro absorptionmodulator or electro optic modulator, or a Mach-Zehnder. In an example,the amplified modulation format is selected from NRZ format or PAMformat. In an example, the phase modulation format is selected from BPSKor nPSK. In an example, the phase/amplitude modulation is QAM. In anexample, the silicon photonic device 1370 is configured to convert theoutput data into an output transport data in a WDM signal. In anexample, the control block 1340 is configured to initiate a laser biasor a modulator bias. In an example, the control block 1340 is configuredfor laser bias and power control of the silicon photonics device. In anexample, the control block 1340 is configured with a thermal tuning orcarrier tuning device each of which is configured on the siliconphotonics device. In an example, the SerDes block is configured toconvert a first data stream of N into a second data stream of M.

FIG. 14 is a simplified block diagram of data flow according to anembodiment of the present invention. As show is a stream of incomingdata, which processed through multiple blocks. The blocks include, amongothers, forward error correction 1410, and other encoding, multi-levelcoding 1420, pre-compression, and digital to analog coding. The blocksalso include non-DSP forward error correction 1430, and a blockcorresponding to a laser diode or driver 1440, among others. In anexample, in the absence of a FEC from a host process, techniques includeuse an FEC internal to the CMOS chip. In an example, FEC can be stripedacross each or all of data lanes. Of course, there can be variations,modifications, and alternatives.

FIG. 15 is a simplified diagram illustrating a redundant laserconfiguration 1500 at a drive stage according to an embodiment of thepresent invention. In an example, the invention provides an integratedsystem on chip device 1510 having a redundant laser or lasers configuredfor each channel. The device 1510 can have a mod driver array 1520 and aTIA/LA array 1521. In an example, the device 1500 has a plurality oflaser devices configured on the silicon photonics device. At least apair of laser devices 1530, 1531 is associated with a channel andcoupled to a switch 1550 to select one of the pair of laser devices tobe coupled to an optical multiplexer to provide for a redundant laserdevice.

FIG. 16 is a simplified diagram illustrating a built-in self test usingan optical loop back according to an embodiment of the presentinvention. As shown are a TX multiplexer 1610 and an RX multiplexer 1620for a silicon photonics device. In an example, the present inventionprovides an integrated system on chip device having a self test using aloop back technique. In an example, the device has a self-test blockprovided on the substrate. In an example, the self test block isconfigured to receive a loop back signal from at least one of thedigital signal processing block, the driver module, or the siliconphotonics device. In an example, the self test block comprises avariable output power switch configured to provide a stress receivertest from the loop back signal. Also shown is an isolation switch 1640between RX and TX. Optical couplers 1630 and 1631 are coupled to the TXMux and RX Mux, respectively, as well as the isolation switch 1640.

In an example, the present technique allows a loop back test capabilityon the device, which is now a silicon photonic application specificintegrated circuit or a communication system on chip device, asdescribed. In an example, the technique is provided for diagnostic andsetup during power up sequence. In an example, an optical tap coupler onthe output side connected to the input side as shown. In an example asshown, x (e.g., <10%) is selected to reduce and/or minimize an impact anoutput power as well an impact at the input power given that input poweris generally much lower than the output power. In an example, to preventcrosstalk in the present loop back path, an isolation switch has beenconfigured as shown. In an example, without the isolation switch thereis undesirably direct crosstalk between the output and input as shown.In an example, about 30 dB isolation is included to prevent deleteriouseffects of coherent crosstalk. Of course, there can be variations.

FIG. 17 is a simplified diagram illustrating a built-in self testconfigured for optical testing according to an embodiment of the presentinvention. In an example, the present invention provides an integratedsystem on chip device having a built-in self test technique. As shownare a TX multiplexer 1710 and an RX multiplexer 1720 for a siliconphotonics device 1700. A broad band source 1730 is coupled to each ofthe multiplexers. Multiple sources can also be included. In an example,the device has a self test block configured on the silicon photonicsdevice and to be operable during a test operation. In an example, theself test block comprises a broad band source configured to emitelectromagnetic radiation from 1200 nm to 1400 nm or 1500 to 1600 nm toa multiplexer device. In an example, the broad band source 1730 can bean LED or other suitable device. The device also includes a self testoutput configured to a spectrum analyzer device external to the siliconphotonics device. In an example, the technique can be provided during acalibration process. That is, if after calibration, a center λ of eachmultiplexer changed, the present technique including built-in lightsource will quantify or indicate the change in an example. In anexample, the broadband source in silicon photonics is a light sourcewith no optical feedback, although there can be variations.

FIG. 18 is a simplified diagram illustrating wavelength tuningconfigured to silicon photonic device according to an embodiment of thepresent invention. In an example, the present tunable laser uses a setof rings or gratings with resonant frequencies that a slightlydifferent. In an example, the technique use a vernier effect to tune thelaser over a wide frequency range—limited by the bandwidth of the gainregion. In an example, the vernier desirably would be held in lock withrespect to one another. In an example, the technique uses a ditherfrequency on one of the biases (e.g., heater) and lock the ring to themaximum transmission of the second ring or grating, although there canbe variations. As shown in graph 1901, resonant combs are generallymisaligned in an example. When tuned, thermally or otherwise, techniquescan be used to selectively align one of the combs to another comb orspatial reference as shown in graph 1902. In an example, to maintainalignment, the technique dithers the signal to one of the rings. Ofcourse, there can be variations, alternatives, and modifications.

FIG. 19 is a simplified block diagram of an interface for a siliconphotonics device according to an embodiment of the present invention. Inan example, the interface is provided to communicate between the controlblock and the silicon photonics device. The interface includes one ormore of a modulator bias voltage input, a laser DC bias current input, aphotocurrent or set output, a power monitor current/voltage output, aphotodetector bias input, a heater current/voltage input, a photocurrentfrom input signal or set output, a wavelength monitorvoltage/current/resistance output, among other elements. Of course,there can be variations.

FIG. 20 is a simplified diagram illustrating a laser configuration at atransmitter side of a silicon photonics device according to anembodiment of the present invention. As shown are a plurality of laserdevices 2120 numbered from wavelength 1 to n, each of which has amodulator device 2140, and are collectively coupled to a spectralmultiplexer 2160. Each of the laser devices 2120 are coupled to a pairof control blocks, such as blocks 2111 and 2112, and monitor blocks2130. The spectral multiplexer 2160 is coupled to a fiber interface2170. As shown is a broad band source 2150, as previously noted.

FIG. 21 is a simplified diagram illustrating a laser configuration at areceiver side of a silicon photonics device according to an embodimentof the present invention. As shown are a plurality of detectors 2210numbered from wavelength 1 to n, each of which has a oscillator device2230, and are collectively coupled to a spectral multiplexer 2250. Eachof the photodetector blocks 2210 can be coupled to hybrid blocks 2220.The spectral multiplexer is coupled to a fiber interface 2260. As shownis a broad band source 2240, as previously noted.

FIGS. 22 and 23 are simplified diagrams illustrating a hybrid lightsource for a silicon photonics device according to an embodiment of thepresent invention. As shown in FIG. 22, device 2301 includes a siliconsubstrate 2310 for photonics devices, and an overlying buried oxideregion 2320. In FIG. 23, device 2302 includes the same substrate 2310and buried oxide region 2320, and also includes an overlying crystallinesilicon material 2330 configured for a waveguide or guides. Of course,there can be other variations, modifications, and alternatives.

FIG. 23 is a simplified diagram illustrating a wavelength control andlocking configuration with a silicon photonic device according to anembodiment of the present invention. As shown, device 2401 shows a laserdevice coupled to control blocks, and a modulator block. Drivers #1 and#2 are coupled to the control blocks #1 and #2. A fixed bias setting iscoupled to driver #2, whereas a variable bias setting is coupled todriver #1. The monitor block coupled to the modular and laser device isalso coupled in series to a photocurrent detect circuit to TIA withbandwidth 2f-4f block, where the dither frequency is f, a minimum detectcircuit to derivative block, and the variable bias setting block. Graph2402 shows the signal at the monitor #1 block when dither is applied,showing the derivative signal in the bottom graph. Graph 2403 shows theeffect of applying dither to one comb on the wavelengths produced. Thisself-test configuration can also be used in the detections of the oddharmonics.

FIG. 24 is a simplified diagram illustrating a wavelength control andlocking configuration with a silicon photonics device according to analternative embodiment of the present invention. The device of 2501shows a similar configuration to device 2401 of FIG. 24. Here, thephotocurrent detect circuit includes a TIA with BW up to 2f or 4d with aband pass filter at 2f or 4f (which can be 2 kf, where k=1, 2, 3, etc.)Graph 2502 shows the signal after the detect circuit when dither isapplied to one of the controls. Graph 2503 shows the application ofdither to one comb, similar to graph 2403 of FIG. 23.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

1-20. (canceled)
 21. A method for processing optical signal, the methodcomprising: receiving an incoming signal; generating a driving signalbased on the incoming signal; receiving a light from a light source;generating a bias signal for minimizing a noise variance that isproportional to 2√{square root over (nΔP_(ASE))}, wherein nΔ is a signallevel n and P_(ASE) is an Amplified Spontaneous Emission Power;modulating the light to generate a light signal using the bias signaland a raised sine transfer function; amplifying the light signal; andfiltering the amplified light signal.
 22. The method of claim 21 whereinthe incoming signal comprises differential input signals.
 23. The methodof claim 21 wherein the incoming signal is generated using an arbitrarywaveform generator.
 24. The method of claim 21 further comprisingapplying a compression function to the bias signal.
 25. The method ofclaim 24, wherein the compression function causes a modulation signal toexhibit an expanded top eye opening region and a compressed bottom eyeopening region.
 26. The method of claim 21 wherein the light ismodulated by a Mach Zehnder Modulator.
 27. The method of claim 21further comprising transmitting the light signal to an Erbium-dopedFiber Amplifier via an optical link.
 28. The method of claim 21 whereinthe bias signal comprises an off-quadrature bias.
 29. The method ofclaim 21 wherein the light signal comprises a PAM-4 signal.
 30. A methodfor processing optical signal, the method comprising: providing adriving signal; receiving light from a light source; processing apulse-amplitude modulation (PAM) signal using a Mach Zehnder Modulator(MZM), the MZM being characterized by a raised cosine transfer function,the PAM signal being characterized by a top eye opening region and abottom eye opening region; generating a bias signal for minimizing anoise variance of the PAM signal, the bias signal causing a compressionof the bottom eye opening region, the noise variance being proportionalto 2√{square root over (nΔP_(ASE))}, wherein nΔ is a signal level n andP_(ASE) is an Amplified Spontaneous Emission Power; and modulating thelight to generate a light signal using at least the driving signal andthe PAM signal.
 31. The method of claim 30 wherein the bias signalfurther causes an expansion of the top eye opening region.
 32. Themethod of claim 30 further comprising attenuating light signal.
 33. Themethod of claim 30 further comprising amplifying the light signal usingan erbium doped optical amplifier.
 34. The method of claim 33 furthercomprising filtering the amplified light signal.
 35. The method of claim30 wherein the PAM signal comprises a PAM-4 signal.
 36. The method ofclaim 30 wherein the bias signal comprises a DC compression function.37. The method of claim 36 wherein the DC compression function comprisesan inverse raised sine function.
 38. The method of claim 30 furthercomprising applying the bias signal to the PAM signal in a downwarddirection.
 39. The method If claim 30 wherein: the PAM signal comprisesfour levels; the bias signal equalizes noise distribution among the fourlevels.
 40. A method for modulating optical signals, the methodcomprising: providing a light; providing a PAM signal, the PAM signalcomprises four amplitude levels; generating a bias signal, the biassignal based on a DC compression function for minimizing a noisevariance among the four amplitude levels of the PAM signal, the biassignal causing a compression of the bottom eye opening region, the noisevariance being proportional to 2√{square root over (nΔP_(ASE))}, whereinnΔ is a signal level n and P_(ASE) is an Amplified Spontaneous EmissionPower; modulating the light to generate a light signal using the PAM-4signal and the bias signal.